Machine-to-machine (M2M) communications, also referred to as machine-type communications (MTC) in 3GPP (3rd Generation Partnership Project), is a type of communication that is expected to expand, potentially rapidly, in the near future. With MTC, machines may locally or remotely communicate directly with one another and may be employed for various applications including for example for smart homes, security and surveillance, smart/remote metering, fleet management, remote healthcare, access network operation management, manufacturing automation, etc.
Wireless devices often make use of so-called discontinuous reception or DRX in which the device is only periodically receptive to incoming control signals from the network (including in particular paging messages). The device at least partially powers down when not expecting to receive incoming control signals, for example by powering down a radio system of the device, which saves power and therefore extends battery life in battery-operated devices. The term “radio system” is typically used in this specification to refer to one or more of the radio front end, antenna(s), and relevant processing circuitry and software required for transmission/reception in a wireless device. In at least some circumstances, the term “radio system” is used to refer to all of such components. The time period of this “ordinary” DRX, i.e. the length of time that the device is (at least partially) powered down or “asleep” between reception periods, is typically quite short, of the order of a few seconds (say 10 seconds or so) at most. As a particular example, the maximum specified default paging cycle value in radio frames in Technical Specification 36.331 in 3GPP E-UTRAN (Evolved Universal Terrestrial Radio Access Network) is 2.56 s, and can be configured for the RRC_IDLE and RRC_CONNECTED states, where RRC_is Radio Resource Control. However, shorter time periods may be used, specific examples including 320, 640 and 1280 milliseconds.
These relatively short DRX time periods are well suited for use by personal wireless devices (including for example mobile devices including mobile or cell phones (including so-called “smart phones”), personal digital assistants, pagers, tablet and laptop computers, content-consumption or generation devices (for music and/or video for example), data cards, USB dongles, etc., as well as fixed or more static devices, such as personal computers, game consoles and other generally static entertainment devices). Users of such devices will typically want to be made aware rapidly of an incoming voice call, or SMS text message, or email or the like.
However, for machine-type communications (MTC) in machine-to-machine (M2M) communications in particular, a much longer “extended” DRX time period has been proposed, largely to keep down the frequency of paging messages and other system signals being sent and therefore to keep down the general volume of network traffic, and also to keep down power consumption, which again is important for battery-powered devices. The extended time period may be at least several minutes, but is typically an hour or several hours, or even 24 hours or even several days. As can be seen, the extended DRX time period is likely to be at least 1000 times longer than an ordinary DRX time period. For a specific example relevant to 3GPP, see the contribution 52-112592 in 3GPP TSG SA WG2 (Technical Specification Groups Service and System Aspects Working Group 2). However, the use of an extended DRX time period gives rise to a number of different problems.